Review: TruTune Suspension Inserts Unlock More Travel

Apr 26, 2023
by Seb Stott  
photo



TruTune is a plug-in suspension modification that takes the place of a volume spacer in your fork but has the opposite effect. When I first heard about it, I thought it was a joke, but after talking to the engineers at Carbon Air, the company behind TruTune, I realised the physics was sound. Now I've had the chance to ride it and, at the risk of giving away the ending of this review too soon, it does what it promises.

TruTune Details

• Makes air-sprung forks less progressive (the opposite of volume spacers)
• Fits Fox 32, 34, 36, 38 & RockShox 32, 35, 38 mm forks.
• Price: £120 GBP
• Money-back guarantee
trutune.co.uk



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What is it?

In a sentence, TruTune doe the opposite of a volume spacer. I wrote a whole article about how exactly it does this, but the short version is that it's made of activated carbon, which is like a really fine porous sponge with a crazy high surface area. Air molecules stick to the surfaces of its tiny crevices and pack together more tightly than in empty space. As the air pressure increases, they pack together even tighter, so essentially, each cubic centimeter of activated carbon acts like two cubic centimeters of empty space. This effectively increases the volume of the positive air chamber, reducing the compression ratio.

The result is that your air spring is more linear than if it had no volume spacers in it at all. Previously, the tuning options for volume spacers have been 0, 1, 2, 3 etc., but now that range of options has been extended to include negative numbers. It's complicated to say how far into the negative it goes, but the TruTune insert I have is equivalent to removing 3-6 volume spacers, depending on the suspension speed. TruTune also make a "short" version which is roughly equivalent to -2 to -4 volume spacers.



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The more travel you have, the fewer volume spacers you need; with modern single crown forks reaching 190 mm travel there is more call to go beyond zero volume spacers.

Who's it for?

Obviously, this isn't going to be useful for everyone - if you need volume spacers to avoid bottoming out then you have no need for this. But increasingly, fork manufacturers have been setting aside more of the available space in the air-side leg for the negative chamber (below the piston) in order to make forks softer at the start of the travel and firmer in the middle. The fact that air springs are usually much stiffer at the start of the travel than in the middle is arguably their biggest downside compared to coil, and increasing the negative spring volume helps remedy this.

But increasing the negative volume (which usually necessitates decreasing the positive volume as there's only so much room inside the fork) makes the fork more progressive. And so, in recent years forks have generally got more progressive. At the same time, long-travel single crown forks (with 170-190 mm travel) have become more common, and increasing the travel makes it much harder to use all of it.

So now more than ever, there are forks that are simply too progressive for some riders. TruTune claims to address this.



photo

Does it work?

Installing the insert is no different to fitting a volume spacer - it just screws onto the bottom of the top cap. To check if it works, I set a 190 mm RockShox Zeb with no volume spacers to 70 psi. By bouncing on the fork as hard as I could on flat ground (I call this the "bounce test"), I was able to use 133 mm of travel. The amount of travel I can access in this test is surprisingly consistent. I repeated the test with TruTune installed and got to 139 mm. This may not sound like a very big difference, but the deeper you go into the travel, the more pronounced the effect becomes - (that's the point).

photo
According to this graph from TruTune's website, the insert in a RockShox Pike reduces the ramp-up of force towards the end of the travel significantly but doesn't make that much difference in the middle of the travel (roughly the opposite of adding two volume spacers). By the way, the reason this graph shows a loop rather than a single line for each volume spacer setting is that the force was measured on compression and rebound, and rebound forces are always lower due to friction and heat loss (see below).

On the trail, I was consistently getting more travel out of the fork, and it was less harsh (more like a downhill coil fork) on big hits. Of course, there was also less support when deep into the travel, but I was able to use a little more air pressure and more compression damping without excessive harshness, and with the 190 mm RockShox Zeb on a Pole Voima eMTB, the progression of the front matched the rear better - without the insert, there was a noticeable ramp of force at about two-thirds of the travel in the fork, which wasn't matched at the rear. In that context, adding the TruTune insert improved the ride noticeably, making the bike feel more balanced and even more forgiving on the rough descents where it was most at home. Although the fork was noticeably softer, I wasn't bottoming out unduly, and I didn't need to compromise on sensitivity to avoid bottom-outs.



photo
Image from TruTune.co.uk

Nerd Section: reducing speed sensitivity

TruTune claim that their product doesn't only reduce progression in the fork, but also reduces the effect of compression speed on suspension stiffness. I explained this concept in more detail in the first look article, but essentially, when air is compressed quickly it gets hot (this is why your pump gets hot when you inflate your tires quickly, or how a diesel engine ignites its fuel without a spark); and when air gets hotter in a fixed volume, the pressure increases.

Normally, the heat that's generated in your air spring as it compresses has time to escape into the walls of the fork, but if the fork compresses quickly, the heat can't escape in time, so the pressure becomes higher than normal for a given point in the travel. That means the spring provides more force when it's compressed quickly versus slowly. This extra force can be as much as 40%.

Whether this is a bad thing is up for debate, but it certainly can contribute to air springs lacking support during slow-speed compressions such as braking and cornering while feeling harsh and being unable to use all the travel on fast, high-frequency hits like slamming into a curb.

Trutune say that because their insert has a high surface area and a lot of mass compared to the air in the spring, it absorbs the heat generated during fast compressions, and releases it during rebound, reducing the extra force required to compress the fork quickly.

In the chart above they plot the measured air pressure (which is a proxy for spring force) against travel as the fork is cycled through its travel first slowly then faster. This creates a loop in the curve because the pressure is lower during rebound than compression, but as the speeds increase, the force required to compress the fork increases dramatically with nothing in the fork, but more modestly with TruTune installed - hence the black lines keeping closer together than the red lines.

To simplify things, Trutune tells me that their standard insert is equivalent to removing three volume spacers at very low speeds, and up to six at high speeds. TruTune also offer a "short" option which is roughly equivalent to removing two volume spacers at low speed and four at high speed.

If you think that sounds like you're going to be bottoming out all the time, well yes that is a possibility if you're using close to full travel already. But it's worth pointing out that the situations which cause the fork to bottom out (such as the G-out at the end of a rock roll) aren't necessarily the ones that cause the fastest compression speeds (eg. hitting a curb-sized rock at pace), So the effect on bottoming-out is not the same as removing six volume spacers permanently. Plus, on those fast hits, you're still getting more force than on slower hits, just not as much additional force as you'd get in a standard air spring. Remember that with a coil spring, the stiffness doesn't increase at all with compression speed or with travel, yet people who fit coil conversions aren't necessarily bottoming out all the time.

The graph above is from TruTune and I don't have the equipment to verify it, but on the trail, you can certainly notice there's a more forgiving feel on big hits. I can't say how much of that is due to reduced speed sensitivity and how much is simply due to the lower compression ratio.



What's the bottom line?
bigquotes While it's tricky to get your head around how it works, TruTune does a very simple job: it makes air-sprung forks less progressive. In that sense, it does what it sets out to do, allowing access to more travel, with less harshness on big hits, albeit at the necessary expense of reduced support and bottom-out resistance. Obviously, that isn't something everyone needs. But because some modern long-travel forks are very progressive, and given they're not exclusively ridden at Rampage, plenty of riders could benefit from the ability to go more linear than zero volume spacers. Seb Stott




Author Info:
seb-stott avatar

Member since Dec 29, 2014
287 articles

244 Comments
  • 220 1
 I just want to go for a bike ride without inserting something.
  • 132 0
 That's not the feeling I got after paying for my new bike...
  • 9 11
 Insert the saddle in your bike.
  • 17 0
 What kind of bike have you been riding? www.youtube.com/watch?v=fGKR1Z1lRik
  • 55 3
 Buy a coil fork and you'll never have to worry about any unnecessary inserting.
  • 24 2
 @fartymarty: These days to achieve that you have to buy a fork you like, and then spend several hundred dollars more to irreparably convert it to coil. Ask me how I know...
  • 11 0
 @Grizzly134: how do you know?
  • 1 0
 @ReformedRoadie: you beat me to it.
  • 2 1
 @Grizzly134: I'll bite. I'd like to know your experience
  • 13 0
 @Grizzly134: Why not just buy a coil fork to start with?
  • 4 1
 @93EXCivic: Z1 or MRP Ribbon are the only real mainstream choices?
  • 12 0
 @93EXCivic: having just bought a helm coil, it is very refreshing to get on my bike and be absolutely certain the spring rate has not changed due to any number of variables (placebo included)
  • 2 0
 These comments are fire!
  • 6 1
 @fartymarty: This comment should have way more upvotes. All I've been hearing for the last 10 years or so is "how much air suspension has improved in recent years". I've tried a bunch of shocks/forks over the last 20 plus years of riding. And I still have to say, the best feeling suspension I've ever ridden was my Pushed Fox 36 Van/DHX-RC4 setup.
  • 7 0
 I don’t need to use all my suspension travel all the time
I need to use the right amount in the right terrain.
  • 2 1
 @fartymarty: Except when you gain or lose weight and now you have an unnecessary spring inside.
  • 2 1
 @hrubarb: Damping arguably matters more than spring rate, so there's something you can worry about instead. You're welcome.
  • 5 0
 @fartymarty: Bomber Z1 coil, best fork out there at the moment, and no unnecessary inserting of third party coil conversions
  • 2 0
 There's always a fascination of inserting something into some hole.
  • 2 0
 @jlauteam1: and Ohlins...
  • 2 0
 @jlauteam1: Cane Creek Helm coil is pretty good.
  • 9 0
 Buy Manitou!
  • 1 0
 MRP Ribbon coil and Formula Selva coil are other easy to find options
  • 1 0
 @93EXCivic: Because the damping I want is not available with a coil. My coil options are all somehow compromised. I actually own a coil fork from a smaller company which offers it in coil natively, and the overall performance just is not very good. Not very plush. The addition of the coil helped out, but an out of the box Pike is a better ownership and riding experience.
  • 2 0
 @Grizzly134: if you do it with Ohlins you can convert back to air
  • 2 0
 @davar16: Its pretty simple, really. I prefer Fox damping, specifically the Grip 2. I'm heavier, so while some of my lighter friends prefer the more open feel of say, one of Rockshox's Charger dampers, I like the feeling that my Fox moves on the smallest impacts, but still offers a damped feel for that small movement. Plush, but controlled is how I'd describe it.

I've owned or tried the readily available coil forks on the market, and they do not feel good to me (notably missing was Ohlins, because I'm not made of money). So where I ended up was on a Fox 36 with the Grip 2 damper and a Smashpot coil conversion kit from Vorsprung. I've owned this fork from new, and I believe it is a 2019 or so. It doesn't have those burping ports on the back of the legs.

Side Note: I also own a late model Fox 38. While this fork ostensibly has the same damper, I much prefer this fork, even in its air version, to the coil converted 36. Supposedly the difference between the forks stock is air piston diameter and the resulting seal friction is reduced in the 38, but my coil kit on the 36 should eliminate that souce of a difference in feel. I think I'm just going to deal with the weight and ride the 38, if I condense my fleet moving forward.
  • 1 0
 @SonofBovril: True. And also true for the 38. But that wasn't the fork I had, and the reviews of the Ohlins, while positive, seem to all place it slightly behind the Fox for my needs. That said, Ohlins will be my next rear shock purchase, whenver that happens.
  • 1 0
 @Grizzly134: I have Ohlins coil front and rear. suffer from arthritis and other stuff that was making riding painful. I'd changed bars to the One up and even added rev grips. The fork was a total game changer, smashing times on trails Ive been riding for 10 years. the rear is just sublime too.
  • 2 0
 @vtracer: Manitou. Dorado. Comp. Inverted coil
  • 1 0
 @Grizzly134: Thanks for sharing! I have a DVO Onyx that always feels sticky. I've considered the Smashpot, but it's expensive and I don't know if it'll even give me what I want.

It's also interesting to hear you like the 38 (air) more than your 36 coil. I have a RS Domain on my other bike and it feels pretty good/plush to me despite having a "cheap" damper. I'm also heavy rider. I wonder if those stiffer stanchions are the real key. Supposedly they reduce flex and thus reduce binding on the bushings--a problem you would still get on coil.

(As a side note, I just sent my Onyx in for a potential warranty repair. Hopefully they'll find something wrong, like hte bushings, and it'll come back feeling amazing)
  • 173 0
 Could I run this in conjunction with 3 volume spacers to have no effect on performance but make by fork more expensive and slightly heavier?
  • 15 1
 In my opinion, the selling point of this product is the removal of the adiabatic effect. If you wanted the same progression without the harshness or lower predictability associated with air suspension, this would be it
  • 1 11
flag spankthewan (Apr 26, 2023 at 10:29) (Below Threshold)
 @skimgosu: Put some wire mesh in with your volume spacers, and the effect would be similar.
  • 3 0
 @skimgosu: What simp isn't running with Push's new Bunsen insert yet?!
  • 34 1
 That will get you a bit of an increase, but you could also go the Vorsprung route and fit the Smashpot coil conversion, the Secus air chamber extension and then search out a progressive spring to get back to the full air fork feel.

That way you could achieve nothing but also spend a lot more AND add a load more weight; triple-win.
  • 3 2
 Sounds like a Matt Beer idea.
  • 3 0
 @Woody25:
I like your thinking. You've then also got the added benefit of being unable to revert back to an air spring after realising the set-up is just too good.
  • 11 0
 @sweatyseagull: I hadn’t thought of that but it’s an excellent point. This kind of setup will be ideal for a morning on the blues running 75% sag followed by an afternoon on the forums opining about how your suspension still isn’t right and perhaps it’s time for a shift to a full EXT setup
  • 1 0
 @skimgosu: It couldn't be infinite though - eventually the insert would heat up and make it worse! Nowhere 'new' for the heat to go...
  • 1 0
 @DaveRobinson81: I agree with the sentiment. We don't know if the product's performance degrades over the course of an enduro stage. I am simply allured by the prospect of a spring system that feels like a coil but weighs like air.
  • 1 0
 @skimgosu: Fair point - think the ohlins system of 1neg and 2 positive chambers is your best bet overall (I am guessing more consistent than this), or manitou, or buy a runt/AWK for (most) other forks...
  • 55 2
 once in a while you see a product that you didn't know you needed lol!

at 85 kg, I've been struggling to use full travel on my 190 zebs ( with the correct sag and 0 tokens )
  • 17 0
 This was the exact feedback the dude giving the ZEB vs. 38 review made.
  • 7 2
 Have you tried compressing your Zeb 60mm or so then equalising the air in the outer fork legs (by valve or zip tie method)? This will make your fork more linear
  • 1 0
 The progression comes from the outer air spring which is effectively the trapped air in the outer casing legs. If you take all of the air out, then compress the fork fully you will see how much this is adding to the spring rate through the travel
  • 3 0
 I was struggling bottoming out my zeb at 105kg with 20% sag which was below 22 psi of the rockshox recommendation
  • 3 0
 @jaytdubs: The TrueTune seems perfect for the ZEB. Especially if you're running the new air spring or a luftkappe. I think a lot of rider, myself included, run higher pressure in the ZEB to get enough support. This causes the fork to be very progressive even absent any volume spacers. I'd love to try even higher pressure with the TrueTune installed.
  • 5 0
 @notphaedrus: but the vacuum could suck in more dirt and/or slightly reduce travel. AirLink by Everflow will solve that www.everflow.it/webshop/tuning-parts/airlink
  • 66 3
 Have you tried riding terrain which would require 190mm of travel? Wink
  • 7 3
 Maybe shorter travel bike next time? You'd be carrying less weight up hill and getting full use of the travel on the way down. Just a thought.
  • 26 3
 "Struggling to use full travel" could be a symptom of having 190mm of travel but your local trail isn't the Lourdes DH track
  • 16 2
 Lol maybe you don't need a 190 Zeb
  • 1 0
 my experience, Trutune plus 8% psi is the same as correct setup and 1token even how much travel you use on deep hits. makes you enter mid stroke more reduces some fatigue and improves initial traction. currently running without Trutune and 0tokens, reason im not using TruTune just now is i feel you need to tune the HSC/LSC shim stacks to get full potential from the insert. ZEB select+ 170 travel
  • 12 0
 @ryanandrewrogers: i once rode the lourdes downhill track on 2003 90mm travel xc bike. All travel was used
  • 3 1
 @qualms23: 26" wheels? How did you even ride that thing?
  • 1 6
flag Jordmackay (Apr 27, 2023 at 2:34) (Below Threshold)
 @Noeserd: You're doing your sag wrong. Both arms on your bars, brakes on taking all of your weight. feet off the ground
  • 5 0
 @Jordmackay: Yes i know how to do a correct sag Smile
  • 1 0
 @bafo: I’ve not noticed that happening, and I service my lowers every 3 months maximum. It’s not a massive vacuum and don’t forget, it’s sealed anyway other wise it wouldn’t be acting like a second air chamber!
  • 2 0
 @qualms23: my brother did the same, wait, James is that you?
  • 2 0
 @trailchaser91: Jacky boi! I thought you were lost forever in the great flood.. god bless the internet, god bless Pinkbike
  • 1 0
 Compression damping is also a variable - what's your HSC an LSC set to?
  • 1 0
 @notphaedrus: wow that’s interesting. So that air in the lower is independent of air pressure setting. If I understand right you’d push the fork down say 60mm and release using the valves on the ZEB? With no air I have really bounce on the fork to get the travel o ring right to the top.
What a great tip. Does bleeding the lowers with those bleed valves cure it? Thx.
  • 1 0
 @mudfish: yes, if you have bleed ports, just push them. Much easier if you do
  • 35 0
 For lighter riders I can see this being pretty cool. At 125lbs even running 0 spacers I find it hard to use the travel unless I run a lower pressure and have a really soft/diving fork...

Would love to be able to try this!
  • 58 5
 Am I the only one who doesn't want to ever use full travel on my fork? I want that last little bit for big f*ck ups that I do maybe once a year. If your trying to get full travel on your fork every ride it sounds like your stuffing it a lot or almost going over the bars. Maybe it's just the steep trails here but I prefer my fork stiff. But I don't know shit.
  • 9 0
 @BrianColes: Not necessarily being able to regularly bottom out the fork. Just being able to use more of the travel without having to run a super low pressure - basically making it more of a linear spring rate..
  • 2 9
flag ryanandrewrogers (Apr 26, 2023 at 15:59) (Below Threshold)
 @kitagawasan: Sounds like you have too soft a midstroke if your fork is "diving". There's nothing wrong with running low fork pressure as a light rider.

My advice is to run your low-speed compression at least ~50% closed (& high-speed 25% if you have a knob for it) and drop your pressures 5-15 psi. Set your rebound fast, 2-4 clicks from fully open.

You'll have a lot more midstroke support, you'll still rarely bottom out, and the fork will be a lot plusher in the big hits. You might even want a token or two after trying it out. This thing will only make your fork dive even harder, it kills your midstroke support and will make hard braking suck.
  • 3 1
 Just get an awk chickadehill.
  • 16 0
 Does this work indefinitely or do they have a lifespan?
  • 30 0
 Yeah, only rated for 700 years unfortunately.
  • 1 3
 100 hours apparently
  • 12 0
 @antop34: That's not quite right. At least if you're just going of what TruTune say, which is:

"So far, our inserts have individually spent 100+ riding hours in forks without any noticeable changes to performance. Our earliest prototypes have been in forks for over a year and have maintained their adsorptive properties over time. We are continuing to test and monitor their durability and as we learn more about the long term lifespan we will make more information available."

So basically, they're saying AT LEAST 100 hours, but also, we don't know.
  • 5 0
 @Will762: That's also not quite right. At least if you're going off what @bigtim says, which is:

Yeah, only rated for 700 years unfortunately.

So basically, ignore my stupid comment.
  • 3 0
 @bigtim: It might need carbon dating by then!
  • 1 0
 @Will762: cheers for the answer
  • 13 1
 I get the purpose, but doesn't a coil fork do this already? I could understand the reasoning though, because with this you get far more tuning than a coil shock.
  • 14 0
 I think you hit the nail on the head with your second sentence. You get the infinite adjustability of air but the linearity of a coil. A bonus is that I assume it weighs less than the coil, but if you have a 190mm Zeb weight probably isnt at the top of your concern list.
  • 2 6
flag ryanandrewrogers (Apr 26, 2023 at 16:03) (Below Threshold)
 This thing also f*cks your midstroke support.

There are only two kinds of riders who want this: those with a faulty Zeb/38, and those who haven't tried less fork pressure with more compression.
  • 2 0
 @ryanandrewrogers: If you run more pressure the midstroke support is there but without the progression that keeps you from using more travel on the bigger hits.
  • 4 0
 @mtmc99: what if I told you that 190mm Zeb and 160mm Zeb had the same weight?
  • 2 0
 Cheaper than a coil conversion. I love coil forks and have one myself, but I'd love to try one of these.
  • 3 0
 Most coil conversions are also a one way ticket. Having a steel spring banging around inside your stanchion will make it hard for an air piston to seal if you decide to go back.
  • 2 1
 @NickBosshard: They've only durability tested this up to ~100 hours, I'd be very surprised if the charcoal dust within this token doesn't get into the oil of your fork eventually.
  • 1 1
 @chakaping: Not even vaguely comparable to a coil conversion. Yes, certainly cheaper though, it is after all charcoal.
  • 1 0
 @NickBosshard: that's why i put the smaspot on the right leg on my lyrik and swapped the damper to the air side(left).
  • 10 1
 I dropped my Pike and got a DVO Diamond to get rid of the ramp up at the end of the travel. Interesting that Fox shows the same problem. Aren't RS and Fox supposed to be the best, year after year of ceaseless upgrades. The DVO is by the way great off the box, and you can actually easily shim it to your content. Which I did resulting in a wonderfully complaint fork that takes all kind of hits, from tiny to big, uses all its travel, and is never noticed. Finally a fork that works for my 68 Kg weight.
  • 2 2
 What? Dvo has some of the most aggressive tunning stock.
  • 4 0
 @freeridejerk888: DVO is digressive
  • 1 0
 Aren't RS and Fox supposed to be the best.... says who?
  • 1 1
 @honda50r: I’m talking about the damping tune not the air spring. They are very stiff forks. Atleast they used to be. I’m slowly going back to RA from all the quality problems
  • 2 1
 @JohanG: If that were truly the case, then why the market for Manitou, Cane Creek, Ohlins, Formula, DVO, Avalanche, Vorsprung, etc.? That's a rhetorical question.
  • 10 1
 Genuine questions for Trutune/Carbon Air: 1.) Is there any chance that small carbon pieces/dust from the activated carbon will come loose and wind up in the grease/oil on top of the air spring piston? 2.) Have you tested this long term with forks that use oil (i.e. fox fluid) in the air spring, I could imagine that over time the activated carbon might become coated or saturated with this oil and then stop working entirely and actually become a normal volume spacer. Thanks.
  • 3 0
 They SORTA address this in the FAQ on their site. Scroll down, click FAQ. Had the same questions as you. They also speak to long term durability - basically says they are still gathering data on long term durability.
trutune.co.uk/products/insert
  • 1 0
 I believe the oil question will be an issue. Those pores are a sponge and they have a similar make-up to oil--long chain aliphatic, so they will like each other. Activated carbon is what is used to soak up organics from the air (and water) in filters.
The other issue is the time it takes for air to infiltrate the small pores (which will depend on pore size and pore size distribution). Think of trying to blow (or push) air a lot of air (people) through tiny holes (a couple of fire exits).This time component will make the phenomenon they are interested in dependent on fork travel rate--i.e. their cartridge's contribution to a fork's reaction forces will act completely different at different compression speeds/travel rates. The graphs they show for Force vs Travel are likely done at very slow speeds where are can infiltrate the pores easily. They need to show how the Force vs Travel looks for the whole of rates expected for a fork. I'm guessing at for even fairly low compression rates, this pore structure device will be overwhelmed by the air trying to get in and then it will also be too slow to release the internal air on rebound (referred to as hysteresis), thus being ineffective at all but the slowest fork travel rates.
  • 8 0
 so if added to the positive chamber it helps lighter riders, could a similar concept be used in the negative chamber to help heavier riders? they say the negative chambers can only get so big because of the positive chamber getting larger, so theoretically, you could add this to increase the air volume in the negative chamber? please let me know if im being a big dummy and this isnt how any of this works.
  • 3 20
flag skywalkdontrun (Apr 26, 2023 at 8:50) (Below Threshold)
 That's not how it works. Negative chamber is what helps the air spring return from compression.
  • 4 0
 Negative spring should help with breakaway force, right?
  • 1 0
 @skywalkdontrun: no I think you might have it confused, that is not the main purpose of the negative spring. It’s purpose is to reduce the breakaway friction at the beginning of the stroke
  • 14 2
 Would rather eat £120 worth of pie and chips so I wouldn't need this.
  • 29 1
 day in the life of a true brexit geezer
  • 7 0
 At current rates of inflation that'll soon be just two portions.
  • 4 0
 Fish and chips surely? I'm sure (Rockshox) Pike would be good battered...
  • 7 0
 It would always drive me nuts trying to set up my fox fork and not being able to use the last 20mm of travel due to the harsh ramp up without it being super soft off the start. I have switched to Ohlins and find it way easier to set up and actual change the compression on the fly going from steep tech to flow trails.
  • 5 1
 That's a Fox valving problem. Forks like Ohlins and Manitou with well engineered compression dampers don't experience that. Incidentally, the Manitou IRT system gives a perfectly linear spring curve until the hbo kicks in at the end.
  • 4 1
 @JohanG: Couldn't agree more. I don't understand why this 'needs' to exist when a 'dual/twin' positive chamber can do the job with more adjustability. I would recommend a runt or AWK over this product...

I would also like to see negative chamber adjustability like Ohlins on all forks (as I think that's a more appropriate solution than simply increasing negative volume!), but that's just me.
  • 2 0
 I've never found my Ohlins forks easy to achieve full travel but I do agree they have a very controlled and linear feel when compressing. I don't ever feel like they are trying to push back on me. They simply are saying....if you want me to use full travel...you must shred harder!
  • 2 0
 @JohanG: The HBO on the Mezzer is one of the best things I've ever experienced in a fork. Never a harsh bottom-out.
  • 7 0
 So could I just hang a pack of activated carbon in my fork tube and save $150?
  • 6 0
 Good news..YES.
Bought some activated carbon in a pet shop (Aquarium section), put it in a 3D printed canister and voila! Truely works.
  • 3 1
 @schwarzrot: Make sure to make the canister the carbon is kept in air tight, that way it will have the maximum effect
  • 8 0
 Sill wish there were just more coil fork options
  • 5 1
 Been riding a Trutune for nearly a year now. I’m around 80kg and used to ride with 2 volume spacers. I went up about 7psi in a fox 38 and the traction is much better and don’t have harsh bottom outs. I have used it on both normal and ebike and it’s great. When riding with 2 tokens I can feel the difference and it feels much harsher. Would highly recommend getting one.
  • 1 1
 This sounds like what I’m looking for! Nice.
  • 2 0
 Going from 2 tokens to Trutune sounds weird to me. Folk should be coming off no tokens.
  • 9 1
 Mofos want that coil feel but refuse to use a coil.....
  • 4 0
 TBH I'm not the ideal candidate for this, but I'm a sucker for gear and have been using one in my 150mm '22 Lyrik Ultimate since the beginning of the year. Despite the much higher pressure, I like how it makes the fork feel. It's not too harsh off the top, rides higher in the travel over mid-size chunk and has roughly the same level of support in g-outs and on drops. I haven't gone back to my previous settings to compare, but the setup difference between the two is pretty big:

76kg rider + 14kg bike

Before (2 tokens):
80psi
LSC 16
HSC 2
Rebound 8

After (TruTune)
100psi
LSC 9
HSC 2
Rebound 10

For reference: My testing process was to get the sag into the ballpark and then huck myself off a 4-5ft drop repeatedly, using compression damping to stop bottoming out. Next was some more bracketing on a fast, chunky section of trail with some deep compressions. The surprise there was finding myself liking a faster rebound, despite the higher pressures.
  • 2 0
 Why not just take out the spacer and run less psi and have more small bump traction?
  • 1 0
 @freeridejerk888: I've run this fork with no tokens before and the effect of the Trutune is more dramatic.
  • 8 0
 cool mountain bike shit!
  • 2 16
flag ryanandrewrogers (Apr 26, 2023 at 16:10) (Below Threshold)
 $120+ token made of charcoal is pretty lame in my opinion. 5lbs of this "activated carbon" (fancy term for f*cking charcoal) is available on Amazon for $20.

This is a ripoff that will annihilate your mid-stroke support and make your fork dive like a goddamn submarine under braking.
  • 6 2
 @ryanandrewrogers: Give it a rest, you dont' know what you're talking about.
  • 2 0
 @ryanandrewrogers: With less progression, you can run higher pressures with the same forces at bottom out. The higher pressures then give you more midstroke support.
  • 1 0
 @ryanandrewrogers: I didn't realize submarines where susceptible to excessive brake dive?
  • 1 1
 @NickBosshard: Adding pressure on air suspension, regardless of how linear you manage to make it, will not have a proportional effect on mid-stroke support.

When it comes to air forks, mid-stroke support is mostly an effect of damping.

But okay, enjoy the effects of negative four tokens lol It will never be a replacement for an actual quality damper cartridge.
  • 3 0
 @ryanandrewrogers: So you're telling me that this thing, which affects air pressure will ruin your midstroke support, but changing air pressure won't help with support. Makes sense I guess.
  • 1 4
 @NickBosshard: My reasoning is that this product is made for forks that already have poorly optimized dampers for midstroke support, and the graph indicates that TruTune reduces air spring support primarily in the mid- to end-stoke.

So, obviously, a TruTune user would increase their air spring pressure to account for that. But, air suspension does not increase support proportionally with pressure, ask any big boy with an air fork. Only coil springs increase support proportionally with spring rate.

I've messaged Paul Aston for his opinion. Traditionally the only way to get appropriate midstroke support out of an air spring has been heavier damping in the midstroke, which is exactly what the best-reviewed forks on the market do.

This seems like solving one problem at the cost of creating other problems. Especially since I'm skeptical about the long-term durability of something that probably emits carbon dust, and because if I'm to believe this is "speed sensitive" then surely they should have to address what that does when the fork is rebounding as well.
  • 3 0
 i mean i am sure they thought about this, but what if that compacted carbon dust starts to break apart inside your fork? i could see that scratching the inside of your fork legs and then you're pretty much stuck with buying a coil conversion kit or replacing the uppers and the air spring.
  • 3 5
 Probably, it is after all literally charcoal. If I had this (an impossibility considering I like midstroke support) I'd certainly at least do fork rebuilds more frequently. They've only tested it up to 100 usage hours, which is pretty stupid.
  • 5 0
 We now need an article highlighting the benefits of less progressive frame designs, such as the undeservedly dismissed non-linkage single pivot bikes.
  • 1 0
 well... with a progressive frame design you don't need a progressive shock. Linear coil shocks on progressive linkages are the bomb
  • 5 0
 Thanks for the well made article, Seb. I especially like all the graphs with properly labelled axes. The bike industry needs more graphs.
  • 2 0
 You mean more Sram AXS? (I'll get my coat...)
  • 3 0
 Such an interesting product.
Sounds like it does part of the same job as the Vorsprung Secus (more linear), but by increasing the positive rather than negative air volume?
How about an article rounding up all these cunning fork gadgets and explaining what they do @seb-stott ?
  • 2 0
 Trying to get my head round the real world use of this.

I’m a heavy guy at 100kg and find I need to run high pressure to get correct sag on a set of 36s. Zero tokens and still not getting full travel.

I’m thinking this would help me get that last bit of travel if I left psi for sag the same.

If I’m right someone needs to figure out how to do the same to an X2 shock.
  • 2 5
 Are you just riding in a parking lot? Lol. But for real Zeb doesn’t actually bought them out at the same part as fox you can see where it says Max travel on the zeb. You were a good amount more than me and I have absolutely bottomed out by 170 Z countless times. Make sure you’re looking at the right thing and I don’t know anybody that I ride with a zeb who’s running less than two tokens. We are all nowhere near 100 KG as well.
  • 6 4
 IMO you can't really set fork pressure on sag. It's too dependent on head angle when static. It actually sounds to me like you need to add a couple tokens to reinforce the mid-stroke and drop pressure. But obviously that's a matter of experimentation
  • 2 0
 i'm 65kg and blow through my 180mm fox 36 all the time. What are your local trails like?? Lower your low and high speed compression a bit.
  • 2 0
 @freeridejerk888: yeah mate, just commuting and riding to the pub eh. I’m going to assume your suspension setup is pretty different from mine, different strokes for different folks eh. Ramp up with mine is really harsh and can’t get last bits of travel. Creating more positive volume under pressure seems like an elegant solution.
  • 2 0
 @Will762: given it a go. Just harshens up the end stroke.
  • 1 0
 @jdkellogg: TweedValley in Scotland so steeper, medium and low speed. Compression has been tinkered with they are low already.
  • 1 9
flag bigmeatpete420 (Apr 26, 2023 at 10:44) (Below Threshold)
 @Brewdoo: we’ll you didn’t answer anything so I’d guess your just setting it up wrong
  • 4 7
 Run more sag with more compression, or get an aftermarket damper. Coil fork conversion would work too.

This is a $120 piece of charcoal that will absolutely f*ck up your mid-stroke support. If you want a fork that dives like James Cameron then go for it I guess. If you ride steep trails at 100kg you will hate this thing.
  • 2 0
 @ryanandrewrogers: I haven’t tried that. Sacrifice some starting travel like @Will762 suggests but instead of tokens dial in compression. Raise my bars to take up any drop in ride height. I’m going to give that a go.
  • 5 0
 So, some toothpastes have activated charcoal. I'll let you guys know of my findings.
  • 5 0
 Could you just make a top cap that extends a few millimeters more to make a larger air chamber?
  • 9 0
 I just leave the top cap off to maximise the air chamber capacityness, for a truly linear feel.
  • 2 0
 Surely this is the wrong way round. Create something to solve a problem caused by another solution to a problem. If this works as it's meant to, why not add this tech to the normal sized negative spring thereby giving you all the nice soft squishy start, leave a nice big mostly linear positive spring that you can then tune the end progression with tokens...
  • 2 0
 Formula made these little things called neo something or other. I put some in my Pike a few years ago, they were meant to achieve more linear compression. No idea if they worked or not, and they're still in there. I think I paid £30 for 3 little foam bungs of potential snakeoil.
  • 2 0
 Awesome! I want more linearity so that the rebound damping is more predictable. I'm running slower rebound off the top so that I don't get pogo'ed on bigger hits.

It's frustrating to tune the rebound to full slow just so that the spring doesn't overpower the rebound damping when it goes deeper into the travel - but then it's not as supple as I would like (thinking retro-Marz here) in the initial part of the stroke
  • 3 0
 Can confirm secus with trutune is amazing…had to run too much sag with secus to get near bottom out but with trutune it’s perfect…need to add psi for both- I’m running about 30% more than stock. 210lbs 170mm fork.
  • 3 0
 Where this would be really useful is in small shocks where air volume is limited but a more linear spring curve would be nice to have.
  • 2 1
 A lot of comments about how these should be great for lighter riders but I would have thought that really it was great for slower riders. If a heavy guy and a light guy both set their suspension to be at 20% sag (and tweak the damping to their weights) then wouldn't the same size drop or speed of impact into an obstacle will be needed to bottom out their suspension? Am I missing something?
  • 1 0
 F=ma
  • 2 1
 OK, so this would have been perfect on my Pike 160mm. It was wayyy to progressive. Which is probably a part of the reason why they ditch this travel option in the 2023 lineup. BUT, a taller custom top cap that would add volume at the top of the chamber would have done the same thing and for about no added engineering. As for the air heating up thingy, your pump get hot because your compressing a air and pumping it elsewhere. In your fork on the trail, the quantity of air molecule stays the same as it compress an decompress. So yes, it gets hot as is compress, but it gets back at theoricaly the same temperature as it decompress. This is not an isolated system, so yes there is heat buildup from friction of the seals and general movement.
  • 3 0
 I want this, my 180mm yari ramps up way too much, but I don't want to coil it
  • 4 3
 Yari ramps up harshly also due to it's trash damper.
  • 4 0
 @tonit91: what damper?
  • 4 0
 @tonit91: I thought they used magic and prayer to make it down the trail
  • 3 0
 It doesn't ramp up, it hydraulically locks out after a couple of fast hits because the oil can't flow through fast enough. Ask me how I know ;p.

Best setup for the Yari: remove all tokens, increase pressure more than you think you should, let rebound as open as you can handle. Counter intuitive, but it worked for me. The damper will still choke at some point because it can't handle successive hits, but at least the fork rides higher in the travel and feels more active this way. The long term solution is to upgrade the damper if you can (or get a better fork).
  • 1 0
 @justwan-naride: after a year of riding it I can say that this is very correct, just waiting for my Z1 to come in now.
  • 1 0
 Looks like they're working on a version for other forks as well. I'd consider one for my Helm Mk1, which is impossible (for me) to get full travel on. Whether that's a damping issue or an air volume issue i don't know?
  • 1 0
 Ive seen a lot of reports that the longer travel marzocchi coil forks were having significant ramp up due to air, I wonder if something like this would be a good solution to that problem.
  • 5 5
 This idea is genius and probably the innovation of the year. One of the main issues with forks is that the high end forks are designed for racing, so there are issues when using race forks when you are going trail speeds. This goes for the same when you are riding modern geo bikes and not "charging the front" and actively stuffing the the front end into everything. I saw this first hand with my 150 lb buddy riding Sedona on his new Lyric last week. He kept complaining of the fork being harsh, etc. He had the sag right, compression open, etc., but the fork was not totally there for him. The fork probably needed an upgrade on the factory lowers service, but this innovation could be really nice for mortals going trail speeds.
  • 5 0
 How are forks designed for racing exactly?
  • 8 1
 I still can’t get past this. Forks aren’t designed for racing. Forks are designed for selling.

You, me, and everybody else doesn’t get prototype racing suspension.
  • 1 0
 @itslightoutandawaywego: Designed for going fast.
  • 1 0
 @itslightoutandawaywego: Dampers could be tweaked and prep might be more exhaustive, but yeah, they are the same forks as the LBS.
  • 4 0
 @itslightoutandawaywego: Bingo. this has been a problem since 2014, when RS started basically making the Pike as a "one chassis for all" (keeping in mind that at the time, most bikes above 160 were running DH forks, and we were still a few years from the Zeb.) They did this by compromising negative air spring design (every fork has the same chassis, therefore the same location for the air transfer port, therefore the same negative spring size. prior to the Pike, forks were using a coil negative spring, which can be tuned by travel, or for rider preference, and critically, without changing the size of the positive air spring.)

They didn't do this for performance. they did it to lower the cost of making the fork, and make that fork marketable for a larger range of bikes. All Pikes, Zebs, 34s, 36s, etc etc etc of any travel are the same except for the length of the air shaft and number of tokens installed (caveat: Fox has been known to not make all stanchions the same length within a chassis model, but the concept is the same.)

and then they came up with a slick marketing strategy for the method they came up with to fix the problem they created: one positive air spring size does not work for a fork that can come in both 160mm and 80mm travel. but if we call them "tokens" and tell people they're for "tuning your progression" then we can pretend this isn't a hack to fix the problem. and in their defense, it isn't even entirely untrue, but they marketed the hell out of it.

On the face of it, none of this couldn't work. but it's a compromise, especially on the longest travel setting, where it's hard to get enough volume for the positive spring. and at least in RS's case, it forced them into some damper compromises as well, especially in the first gen charger. if you liked that progression, it felt fine, which is why there were so many rave reviews at the time. but if you liked a more linear fork feel, the self-equalizing air spring has been a cancer on fork design since it was introduced.

and that's ignoring the lubrication compromises that affect all users.
  • 4 0
 Seems like a weird use for the hot dog chamber, but OK
  • 3 1
 If you are a candidate for this insert... you should just buy an Ohlins or DVO fork... sell you RS or Fox fork... dont waste money on plastic bits to solve a design issue.
  • 1 1
 But it’s not plastic?
  • 1 1
 I don't believe it is possible to create a "black hole" like this by adding something into an air chamber. It still displaces a sertain volume.
I do believe the Activated Carbon could store and release the air a bit slower and make an sensation of softer, make the fork ride a bit lower in it's travel, as an air damper.
  • 1 0
 Wild. Truetone SAYS a lot of things, and that's a nice graph, but I want to see an indy graph, as Seb's 3 mm difference could be white noise of confirmation bias, and doesn't quite sell it for me.
  • 2 0
 Is making a hole in my volume spacer and filling them up with activated carbon a good idea?
  • 3 0
 I am currently in the process of trying this. And someone already 3D printed a canister/token to fill up with activated charcoal with apparently good results. Experimenting with this will cost you 10€, if you like it and want to go further buy the real thing, that's my thought process anyway.
  • 1 0
 @Balgaroth: who makes these fillable tokens?
  • 1 0
 @Rukman: that guy did it for himself as a DIY project, he is a frame builder from Switzerland you can find him on IG under Schwarzrot Cycles. His steel FS is pretty cool too.
  • 2 0
 TruTune have a stand at this weekend TweedLove festival, hope to talk to them there and hopefully get one for my Zeb
  • 2 3
 "The fact that air springs are usually much stiffer at the start of the travel than in the middle is arguably their biggest downside compared to coil, and increasing the negative spring volume helps remedy this."

No, increasing the negative spring force, which is done with pressure not volume, helps remedy this. Just like increasing the the spring force of a coil negative, like DVO's OTT Adjustment can do, will decrease the breakaway force of an air positive spring.
  • 3 9
flag ryanandrewrogers (Apr 26, 2023 at 16:50) (Below Threshold)
 Dunno why you're getting downvotes. People really want to spend $120 on a charcoal f*cking token that makes their fork dive like a sperm whale.
  • 1 0
 I'm kinda unclear does this insert cause more fork dive for a given pressure? Or is it's effect mostly on high speed hits that generate a lot of force?
  • 1 10
flag ryanandrewrogers (Apr 26, 2023 at 16:49) (Below Threshold)
 It will dive like a freaking German Stuka according to the graphs.
  • 1 0
 @ryanandrewrogers: actually look at the nerd section. The way it's written it affects high speed more than low speed and has more of an effect deep in the stroke. The claim is it's speed sensitive.
  • 1 0
 @ashmtb85: It says nowhere that it doesn't affect low-speed compression at all though. Also, when I'm riding steep stuff under brakes, there tend to be bumps too lol

Also, if it's "speed sensitive" as they claim then it is certainly active when the fork is rebounding as well. Seems like a lot of money to spend on something absolutely unproven by any racer, only a claimed "100 hours" of durability testing, and has effects on the rebound that they don't even seem to touch on.
  • 1 0
 I'm surprised no one has mentioned setting up suspension for kids bikes. Those light riders could all benefit from something like this.
  • 3 0
 Is it compatible with Volume spacers?
  • 1 0
 Personally, tire pressure, stiff carbon wheels and or stiff carbon frame add to the frustration of setting up suspension properly. Just a guess !
  • 3 0
 Can it be used as a suppository?
  • 1 0
 Wouldn't it be easier to always keep low and bottom?
Because of the low position, increasing the air pressure increases the harshness.
  • 1 0
 So you could run a higher initial pressure, but get the same bottom out force....nice.
  • 1 0
 This thing is pretty damn interesting. The bit about spring rate changing with speed will certainly take awhile to digest.
  • 3 2
 Accept you don't need to eat all your fork's travel on each ride and save 120 Bucks
  • 22 0
 Accept you don't need to go mountain biking at all and save 6000 bucks
  • 1 0
 So what would happen if you put one of these in a @vorsprung Secus on your fork?
  • 1 0
 Your negative chamber gets so big your forks stretch to 210mm and keeps stretching with every bumps
  • 10 0
 Im no physicist but I cant rule out that this would cause a blackhole to form
  • 1 0
 The FAQ on their website has this to say....

Pairs very well with negative chamber upgrades (e.g. Vorsprung Secus, Everflow Tank) to provide exceptionally linear and consistent feeling through the travel.
  • 1 0
 Revolutionary insert improvement on the way... Hear me out... The inserts go outside of your tires
  • 1 3
 if you have to run more pressure with it, the fact that it reduces your compression ratio wont help you.

people really will buy anything.

its like the whole "bigger tires are faster at the same pressure"...well....yea. but..
  • 2 0
 also, does this work if you use nitrogen in your fork, or only atmosphere?
  • 2 0
 I love the feeling of my geometry changing.
  • 1 0
 I've run one of these in both my Enduro & E-Bike for a year.
It works, it's great, it was a game changer in the Alps.
  • 2 0
 Pick an air volume, be a dick about it.
  • 1 0
 how to do you put something in with feeling up space in it??
  • 1 0
 The physics of this breaks my brain a bit
  • 10 0
 It is pretty easy actually. This antimatter. It absorbs the air in your fork. If you don't inflate your fork, it will create a vacuum which will help you achieve full travel. Just don't ever, EVER, open the air chamber of your fork outside your hermetically sealed lab. It will absorb the earth atmosphere which would create a vacuum so big that it would suck all satellites towards the earth causing a crater so deep it will go all the way through the earth and all water from the oceans would leak out the other side. This could potentially cause invasive species in Aotearoa and we all know they hate that over there. So yeah, keep an eye on that. And of course keep the brain bits together until you've found time to fix it. Sorry, I'm no expert there but if in a pinch, I'd love to help with the brain surgery.
  • 2 0
 @ryan77777 putting a thing in a volume takes less space than nothing in the same volume.
Easy.
  • 1 0
 Wouldn’t wine corks placed inside a sealed bag do this as well?
  • 1 0
 Very cool but I love sproingo boingo. So, no thank you Sir.
  • 1 0
 the TARDIS token.
  • 1 0
 Any plans for the 40?
  • 2 1
 Yay more consumables
  • 1 1
 Since when progressive is bad? I even added 3 tokens
  • 1 0
 I dare you to add one more!
  • 1 2
 a product solving an issue literally no one has.. no one.... not any customer or form has anyone needed this.
  • 1 3
 I have the standard insert for sale for rockshox 35/38 click my username.
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